Information about Metastatic

Classification & external resources

CT scan with metastatic tumour in lung (top right)
DiseasesDB	28954
MedlinePlus	002260

Metastasis (Greek: displacement, μετά=next + στάσις=placement, plural: metastases), sometimes abbreviated mets, is the spread of a disease from one organ or part to another non-contiguous organ or part. Only malignant tumor cells and infections have the capacity to metastasize.

Cancer cells can "break away" from a primary tumor, penetrate into lymphatic and blood vessels, circulate through the bloodstream, and grow in a distant focus (metastasize) in normal tissues elsewhere in the body. Metastasis is considered a hallmark of malignancy. ^[1] All tumors can metastasize albeit to varying degrees, barring a few exceptions (eg. Glioma and Basal cell carcinoma never metastasize).^[1]

When cancer cells spread to form a new tumor, it is called a secondary, or metastatic tumor, and its cells are like those in the original tumor. This means, for example, that if breast cancer spreads (metastasizes) to the lung, the secondary tumor is made up of abnormal breast cells (not abnormal lung cells). The disease in the lung is then called metastatic breast cancer (not lung cancer).

Modes and sites of metastatic dispersal

Metastatic tumors are very common in the late stages of cancer. The spread of metastases may occur via the blood or the lymphatics or through both routes. The most common places for the metastases to occur are the adrenals, liver, brain and the bones. There is also a propensity for certain tumors to seed in particular organs. This was first discussed as the "seed and soil" theory by Stephen Paget over a century ago in 1889. For example, prostate cancer usually metastasizes to the bones. Similarly, colon cancer has a tendency to metastasize to the liver. Stomach cancer often metastasizes to the ovary in women, where it forms a Krukenberg tumor. It is difficult for cancer cells to survive outside their region of origin, so in order to metastasize they must find a location with similar characteristics.

For example, breast tumor cells, which gather calcium ions from breast milk, metastasize to bone tissue, where they can gather calcium ions from bone. Malignant melanoma spreads to the brain, presumably because neural tissue and melanocytes arise from the same cell line in the embryo.^[2].

Cancer cells may spread to lymph nodes (regional lymph nodes) near the primary tumor. This is called nodal involvement, positive nodes, or regional disease. Localized spread to regional lymph nodes near the primary tumor is not normally counted as metastasis, although this is a sign of worse prognosis.

In addition to the above routes, metastasis may occur by direct seeding, eg. in the peritoneal cavity or pleural cavity.^[1]

Factors involved

Metastasis is a complex series of steps in which cancer cells leave the original tumor site and migrate to other parts of the body via the bloodstream or the lymphatic system. To do so, malignant cells break away from the primary tumor and attach to and degrade proteins that make up the surrounding extracellular matrix (ECM), which separates the tumor from adjoining tissue. By degrading these proteins, cancer cells are able to breach the ECM and escape. When oral cancers metastasize, they commonly travel through the lymph system to the lymph nodes in the neck.

Cancer researchers studying the conditions necessary for cancer metastasis have discovered that one of the critical events required is the growth of a new network of blood vessels, called tumor angiogenesis.^[3] It has been found that angiogenesis inhibitors would therefore prevent metastasis. ^[1]

Metastasis and primary cancer

Metastasis theoretically always coincides with a primary cancer. It is a tumor that started from a cancer cell or cells in another part of the body. However, over 10% of patients presenting to oncology units will have metastases without a primary tumor found. In these cases, doctors refer to the primary tumor as "unknown" or "occult", and the patient is said to have cancer of unknown primary origin (CUP) or Unknown Primary Tumors (UPT). It is estimated that 3% of all cancers are of unknown primary origin.^[4] Studies have shown that if simple questioning does not reveal the cancer's source (coughing up blood -'probably lung', urinating blood - 'probably bladder'), complex imaging will not either.^[4] In some of these cases a primary may appear later.

The use of immunohistochemistry has permitted pathologists to give an identity to many of these metastases. However, imaging of the indicated area only occasionally reveals a primary. In rare cases (e.g. of melanoma) no primary tumor is found even on autopsy. It is therefore thought that some primary tumors can regress completely, but leave their metastases behind.

Common sites of origin

• Lung
• Breast
• Skin: Melanoma (other skin tumors rarely metastasize)
• Colon
• Kidney
• Prostate
• Pancreas

Diagnosis of primary and secondary tumors

The cells in a metastatic tumor resemble those in the primary tumor. Once the cancerous tissue is examined under a microscope to determine the cell type, a doctor can usually tell whether that type of cell is normally found in the part of the body from which the tissue sample was taken.

For instance, breast cancer cells look the same whether they are found in the breast or have spread to another part of the body. So, if a tissue sample taken from a tumor in the lung contains cells that look like breast cells, the doctor determines that the lung tumor is a secondary tumor. Still, the determination of the primary tumor can be often very difficult, and the pathologist may have to use several adjuvant techniques, such as immunohistochemistry, FISH (fluorescent in situ hybridization) and others. Despite the use of techniques, in some cases the primary tumor remains unidentified.

Metastatic cancers may be found at the same time as the primary tumor, or months or years later. When a second tumor is found in a patient who has been treated for cancer in the past, it is more often a metastasis than another primary tumor.

Treatments for metastatic cancer

Whether or not a cancer is local or has spread to other locations affects treatment and survival. If the cancer spreads to other tissues and organs, it may decrease a patient's likelihood of survival. However, there are some cancers (i.e., leukemia, brain) that can kill without spreading at all.

When cancer has metastasized, it may be treated with radiosurgery, chemotherapy, radiation therapy, biological therapy, hormone therapy, surgery, laser-immunotherapy, or a combination of these. The choice of treatment generally depends on the type of primary cancer, the size and location of the metastasis, the patient's age and general health, and the types of treatments used previously. In patients diagnosed with CUP, it is still possible to treat the disease even when the primary tumor cannot be located.

Unfortunately, the treatment options currently available are rarely able to cure metastatic cancer, though some tumors, such as testicular cancer, are usually still curable.

References

External links

Medical information about metastatic cancer

• Q&A: Metastatic Cancer – from the National Cancer Institute
• Invasion and Metastases – from Cancer Medicine e.5
• How Cancer Grows and Spreads – an interactive Flash presentation that explores the progression of a carcinoma from a single cell to metastasis; from the research department of Children's Hospital Boston
• Metastasis photo at the Atlas of Pathology website

Charities and advocacy groups dealing with metastatic cancer

• The MetaCancer Foundation – resources and support for metastatic cancer survivors and their caregivers
• Metastatic Breast Cancer Network

Not specifically about metastatic cancer

• Understanding Cancer Types and Staging – a patients' guide at the CancerGuide website
• Cancer Forums – physicians answering questions about cancer

•  • [ e] Pathology: Tumors, neoplasia, and oncology (, )
Benign tumors	Hyperplasia - Cyst - Pseudocyst - Hamartoma - Benign neoplasm
Malignant progression	Dysplasia - Carcinoma in situ - Invasive cancer - Metastasis
Topography	Anus - Bladder - Bile duct - Bone - Brain - Breast - Cervix - Colon/rectum - Endometrium - Esophagus - Eye - Gallbladder - Head/Neck - Liver - Kidney - Larynx - Lung - Mediastinum (chest) - Mouth - Ovaries - Pancreas - Penis - Prostate - Skin - Small intestine - Stomach - Tailbone - Testicles - Thyroid
Misc.	Tumor suppressor genes/oncogenes - Staging/grading - Carcinogenesis - Carcinogen - Research - Paraneoplastic phenomenon - List of oncology-related terms